The combined forces of South Korea and the United States on Monday kicked off their joint annual war game.

The annually-held Ulchi Freedom Guardian (UFG) was scheduled to last through Aug. 31, according to local media reports citing South Korea's military authorities.

The computer-assisted simulation exercise would mobilize about 17,500 U.S. troops, including 3,000 reinforcements from outside South Korea. It was lower than last year's 25,000 U.S. soldiers.

Around 28,500 U.S. troops are stationed in South Korea as a legacy of the 1950-53 Korean War.

From the South Korean side, some 50,000 forces would join the military exercise. It was the same as last year's.